This invention relates generally to cathodic protection of metallic components and/or structures, and more particularly to a system, apparatus, and method of providing cathodic protection to buried and/or submerged metal components and/or structures, such as pipes.
Metallic structures, buried or submerged, are subject to corrosion. As a result, adequate corrosion control procedures are needed to ensure metal integrity for safe and economical operation. In many cases, material selection and coatings are the first line of defense against external corrosion. The function of an external coating is to control corrosion by isolating the external surface of the metallic structure from the environment, to reduce cathodic protection current requirements, and to improve current distribution. External coatings must be properly selected and applied and the coated metallic structures carefully handled and installed to fulfill these functions. Such coatings may provide a moisture barrier and/or electrical insulator and may include polyolefin coatings, epoxy coatings, wax, prefabricated films, and/or coal tar. Additionally, galvanization of steel is often used to protect against galvanic corrosion of metallic structures. Because perfect coatings are not feasible, cathodic protection is often used in conjunction with these coatings.
One area where corrosion of metallic structures is of particular concern is in underground vaults for power cables. These underground vaults not only include cables, but also include cable supports, grounding wires, and other metallic structures such as underground or submerged piping systems. Because the vaults are underground, periods of high humidity and condensation may occur; resulting in atmospheric corrosion and mild and/or moderate degradation of the metallic structures contained within the vaults.
Additionally, the vaults are subject to flooding conditions. If the vaults fail to drain then the vaults fill with high conductivity water and the metallic structures may be subjected to severe galvanic corrosion. Observations of existing vaults has revealed that severe corrosion may exist on metallic cable supports within the vaults after just a few years of installation.
Sump pumps are occasionally employed in vaults to remove the high conductivity water. However, sump pumps may not be effective in cases where water coming into the vaults is constant, for example from a nearby water source, since the vaults can be filled in a short time—days or even hours. Additionally, sump pumps are often disabled due to debris and contaminants that are collected within the vaults throughout the years. Further, environmental restrictions may be an issue in cases where the sump pump in the vault empties the water into the streets and storm drains.
As mentioned above, cathodic protection may be employed to aid in protecting metallic structures. In underground vaults, cathodic protection has been employed by providing a single sacrificial anode disposed at a bottom of a vault. Unfortunately, such cathodic protection is inadequate and/or inefficient in environments where water levels may change due to the current output of the anode being constant, thereby reducing protection during high water levels. Sacrificial anode cathodic protection relies upon energy released from the anode material to polarize the metallic structures within the vault. The act of polarization equalizes the anodic and cathodic sites on the structures, equipment and hardware so that the driving potential is eliminated and the corrosion is reduced or arrested. However, because the water levels within the vaults may change from vault to vault and with the seasons, the current requirements for the cathodic protection system may also change significantly.
Accordingly, there remains a need for a system, apparatus, and method of providing cathodic protection that is optimized for different moisture and/or water levels contained in an underground vault.